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Abstract:

A film that is biodegradable and water-sensitive (e.g., water-soluble,
water-dispersible, etc.) in that it loses its integrity over time in the
presence of water is provided. The film contains a biodegradable
polyester, starch, water-soluble polymer, and plasticizer. The desired
water-sensitive attributes of film may be achieved in the present
invention by selectively controlling a variety of aspects of the film
construction, such as the nature of the components employed, the relative
amount of each component, the manner in which the film is formed, and so
forth.

Claims:

1. A water-sensitive biodegradable film, the film comprising: from about
1 wt. % to about 50 wt. % of at least one biodegradable polyester,
wherein the biodegradable polyester has a melting point of from about
50.degree. C. to about 180.degree. C. and a glass transition temperature
of about 25.degree. C. or less; from about 0.5 wt. % to about 45 wt. % of
at least one water-sensitive starch; from about 0.1 wt. % to about 40 wt.
% of at least one plasticizer; and from about 0.1 wt. % to about 40 wt. %
of at least one water-soluble polymer.

2. The water-sensitive biodegradable film of claim 1, wherein the
biodegradable polyester is an aliphatic polyester, aliphatic-aromatic
polyester, or a combination thereof.

3. The water-sensitive biodegradable film of claim 1, wherein the
biodegradable polyester is an aliphatic-aromatic copolyester.

4. The water-sensitive biodegradable film of claim 1, wherein the
biodegradable polyester has a glass transition temperature of about
0.degree. C. or less.

5. The water-sensitive biodegradable film of claim 1, wherein the
biodegradable polyester has a melting point of about 80.degree. C. to
about 160.degree. C.

6. The water-sensitive biodegradable film of claim 1, wherein the
biodegradable polyester constitutes from about 5 wt. % to about 35 wt. %
of the film.

7. The water-sensitive biodegradable film of claim 1, wherein the starch
constitutes from about 10 wt. % to about 30 wt. % of the film.

8. The water-sensitive biodegradable film of claim 1, wherein the
plasticizer constitutes from about 5 wt. % to about 30 wt. % of the film.

9. The water-sensitive biodegradable film of claim 1, wherein the
water-soluble polymer constitutes from about 5 wt. % to about 30 wt. % of
the film.

10. The water-sensitive biodegradable film of claim 1, wherein the starch
is a modified starch.

11. The water-sensitive biodegradable film of claim 10, wherein the
modified starch is a starch ester, starch ether, oxidized starch,
hydrolyzed starch, or a combination thereof.

12. The water-sensitive biodegradable film of claim 10, wherein the
modified starch is a hydroxylalkyl starch.

13. The water-sensitive biodegradable film of claim 12, wherein the
hydroxyalkyl starch is hydroxyethyl starch, hydroxypropyl starch,
hydroxybutyl starch, or a combination thereof.

14. The water-sensitive biodegradable film of claim 1, wherein the
plasticizer is a polyhydric alcohol.

15. The water-sensitive biodegradable film of claim 14, wherein the
plasticizer is a sugar alcohol.

17. The water-sensitive biodegradable film of claim 1, wherein the
water-soluble polymer is a vinyl alcohol polymer.

18. The water-sensitive biodegradable film of claim 17, wherein the vinyl
alcohol polymer has a degree of hydrolysis of from about 80 mole % to
about 90 mole %.

19. The water-sensitive biodegradable film of claim 1, wherein the film
has a thickness of about 50 micrometers or less.

20. The water-sensitive biodegradable film of claim 1, wherein the film
exhibits a dry ultimate tensile strength of from about 10 to about 80
Megapascals in the machine direction and a dry modulus of elasticity of
from about 50 to about 1200 Megapascals in the machine direction.

21. The water-sensitive biodegradable film of claim 1, wherein the film
exhibits a dry ultimate tensile strength of from about 2 to about 40
Megapascals in the cross-machine direction and a dry modulus of
elasticity of from about 50 to about 1000 Megapascals in the
cross-machine direction.

22. The water-sensitive biodegradable film of claim 1, wherein the film
exhibits an elongation of about 50% or more in the machine direction and
about 50% or more in the cross-machine direction.

23. The water-sensitive biodegradable film of claim 1, wherein the film
exhibits an elongation of about 100% or more in the machine direction and
about 100% or more in the cross-machine direction.

24. A release liner comprising the water-sensitive biodegradable film of
claim 1 and a release agent coated onto a surface thereof.

25. An absorbent article comprising the water-sensitive biodegradable
film of claim 1, wherein the absorbent article comprises a body portion
that includes a liquid permeable topsheet, a generally liquid impermeable
backsheet, and an absorbent core positioned between the backsheet and the
topsheet.

26. The absorbent article of claim 25, wherein the backsheet includes the
water-sensitive biodegradable film.

27. The absorbent article of claim 25, further comprising a release liner
that defines a first surface and an opposing second surface, the first
surface being disposed adjacent to an adhesive located on the absorbent
article, wherein the release liner includes the water-sensitive
biodegradable film.

28. A pouch, wrap, or bag comprising the water-sensitive biodegradable
film of claim 1.

29-48. (canceled)

Description:

BACKGROUND OF THE INVENTION

[0001] Films are employed in a wide variety of disposable goods, such as
diapers, sanitary napkins, adult incontinence garments, bandages, etc.
For example, many sanitary napkins have an adhesive strip on the backside
of the napkin (the napkin surface opposite to the body-contacting
surface) to affix the napkin to an undergarment and hold the napkin in
place against the body. Before use, the adhesive strip is protected with
a peelable release liner. Once removed, the peelable release liner must
be discarded. Conventional release liners may contain a film or paper
coated with a release coating. Such release-coated films or papers,
however, do not readily disperse in water, and as such, disposal options
are limited to depositing the release liner in a trash receptacle.
Although disposing of conventional release liners in a toilet would be
convenient to the consumer, it would potentially create blockages in the
toilet.

[0002] In response to these and other problems, flushable release liners
have been developed that are formed from a water-sensitive film, U.S.
Pat. No. 6,296,914 to Kerins, et al. describes a water-sensitive film
that may include, for instance, polyethylene oxide, ethylene
oxide-propylene oxide copolymers, polymethacrylic acid, polymethacrylic
acid copolymers, polyvinyl alcohol, poly(2-ethyl oxazoline), polyvinyl
methyl ether, polyvinyl pyrrolidone/vinyl acetate copolymers, methyl
cellulose, ethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl
cellulose, ethyl hydroxyethyl cellulose, methyl ether starch,
poly(n-isopropyl acrylamide), poly N-vinyl caprolactam, polyvinyl methyl
oxazolidone, poly(2-isopropyl-2-oxazoline), poly(2,4-dimethyl-6-triazinyl
ethylene), or a combination thereof. Some of these polymers, however, are
not thermoplastic and thus are not readily processed using thermoplastic
film converting equipment. Further, these films are also not generally
biodegradable and may thus further complicate the disposal process.
Certain water-sensitive films also tend to lack good mechanical
properties during use.

[0003] As such, a need currently exists for a film that exhibits good
mechanical properties, and is also biodegradable and water-sensitive.

SUMMARY OF THE INVENTION

[0004] In accordance with one embodiment of the present invention, a
water-sensitive biodegradable film is disclosed that comprises from about
1 wt. % to about 50 wt. % of at least one biodegradable polyester, from
about 0.5 wt. % to about 45 wt. % of at least one water-sensitive starch,
from about 0.1 wt. % to about 40 wt. % of at least one plasticizer, and
from about 0.1 wt. % to about 40 wt. % of at least one water-soluble
polymer. The biodegradable polyester has a melting point of from about
50° C. to about 180° C. and a glass transition temperature
of about 25° C. or less.

[0005] In accordance with another embodiment of the present invention, an
absorbent article is disclosed that comprises a body portion that
includes a liquid permeable topsheet, a generally liquid impermeable
backsheet, and an absorbent core positioned between the backsheet and the
topsheet. The absorbent article further comprises a release liner that
defines a first surface and an opposing second surface, the first surface
being disposed adjacent to an adhesive located on the absorbent article.
The release liner, the backsheet, or both include a water-sensitive
biodegradable film comprising at least one biodegradable polyester, at
least one starch, at least one water-soluble polymer, and at least one
plasticizer.

[0006] Other features and aspects of the present invention are discussed
in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A full and enabling disclosure of the present invention, including
the best mode thereof, directed to one of ordinary skill in the art, is
set forth more particularly in the remainder of the specification, which
makes reference to the appended figures in which:

[0008]FIG. 1 is a schematic illustration of one embodiment of a method
for forming a water-sensitive film in accordance with the present
invention; and

[0009]FIG. 2 is a top view of an absorbent article that may be formed in
accordance with one embodiment of the present invention.

[0010] Repeat use of references characters in the present specification
and drawings is intended to represent same or analogous features or
elements of the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

[0011] Reference now will be made in detail to various embodiments of the
invention, one or more examples of which are set forth below. Each
example is provided by way of explanation of the invention, not
limitation of the invention. In fact, it will be apparent to those
skilled in the art that various modifications and variations may be made
in the present invention without departing from the scope or spirit of
the invention. For instance, features illustrated or described as part of
one embodiment, may be used on another embodiment to yield a still
further embodiment. Thus, it is intended that the present invention
covers such modifications and variations as come within the scope of the
appended claims and their equivalents.

[0012] Generally speaking, the present invention is directed to a film
that is biodegradable and water-sensitive (e.g., water-soluble,
water-dispersible, etc.) in that it loses its integrity over time in the
presence of water. The film contains a biodegradable polyester, starch,
water-soluble polymer, and plasticizer. The desired water-sensitive
attributes of film may be achieved in the present invention by
selectively controlling a variety of aspects of the film construction,
such as the nature of the components employed, the relative amount of
each component, the manner in which the film is formed, and so forth. In
this regard, various embodiments of the present invention will now be
described in more detail below.

1. Film Components

[0013] A. Biodegradable Polyester

[0014] The term "biodegradable" generally refers to a material that
degrades from the action of naturally occurring microorganisms, such as
bacteria, fungi, and algae; environmental heat; moisture; or other
environmental factors, such as determined according to ASTM Test Method
5338.92. The biodegradable polyesters employed in the present invention
typically have a relatively low glass transition temperature ("Tg")
to reduce stiffness of the film and improve the processability of the
polymers. For example, the Tg may be about 25° C. or less, in
some embodiments about 0° C. or less, and in some embodiments,
about -10° C. or less. Likewise, the melting point of the
biodegradable polyesters is also relatively low to improve the rate of
biodegradation. For example, the melting point is typically from about
50° C. to about 180° C., in some embodiments from about
80° C. to about 160° C., and in some embodiments, from
about 100° C. to about 140° C. The melting temperature and
glass transition temperature may be determined using differential
scanning calorimetry ("DSC") in accordance with ASTM D-3417 as is well
known in the art. Such tests may be employed using a DSC Q100
Differential Scanning Calorimeter (outfitted with a liquid nitrogen
cooling accessory) and with a THERMAL ADVANTAGE (release 4.6.6) analysis
software program, which are available from T.A. Instruments Inc. of New
Castle, Del.

[0015] The biodegradable polyesters may also have a number average
molecular weight ("Mn") ranging from about 40,000 to about 120,000
grams per mole, in some embodiments from about 50,000 to about 100,000
grams per mole, and in some embodiments, from about 60,000 to about
85,000 grams per mole. Likewise, the polyesters may also have a weight
average molecular weight ("Mw") ranging from about 70,000 to about
300,000 grams per mole, in some embodiments from about 80,000 to about
200,000 grams per mole, and in some embodiments, from about 100,000 to
about 150,000 grams per mole. The ratio of the weight average molecular
weight to the number average molecular weight ("Mw/Mn,"), i.e.,
the "polydispersity index", is also relatively low. For example, the
polydispersity index typically ranges from about 1.0 to about 4.0, in
some embodiments from about 1.2 to about 3.0, and in some embodiments,
from about 1.4 to about 2.0. The weight and number average molecular
weights may be determined by methods known to those skilled in the art.

[0016] The biodegradable polyesters may also have an apparent viscosity of
from about 100 to about 1000 Pascal seconds (Pas), in some embodiments
from about 200 to about 800 Pas, and in some embodiments, from about 300
to about 600 Pas, as determined at a temperature of 170° C. and a
shear rate of 1000 sec1. The melt flow index of the biodegradable
polyesters may also range from about 0.1 to about 30 grams per 10
minutes, in some embodiments from about 0.5 to about 10 grams per 10
minutes, and in some embodiments, from about 1 to about 5 grams per 10
minutes. The melt flow index is the weight of a polymer (in grams) that
may be forced through an extrusion rheometer orifice (0.0825-inch
diameter) when subjected to a load of 2160 grams in 10 minutes at a
certain temperature (e.g., 190° C.), measured in accordance with
ASTM Test Method D1238-E.

[0017] Of course, the melt flow index of the biodegradable polyesters will
ultimately depend upon the selected film-forming process. For example,
when extruded as a cast film, higher melt flow index polymers are
typically desired, such as about 4 grams per 10 minutes or more, in some
embodiments, from about 5 to about 12 grams per 10 minutes, and in some
embodiments, from about 7 to about 9 grams per 10 minutes. Likewise, when
formed as a blown film, lower melt flow index polymers are typically
desired, such as less than about 12 grams per 10 minutes or less, in some
embodiments from about 1 to about 7 grams per 10 minutes, and in some
embodiments, from about 2 to about 5 grams per 10 minutes.

[0020] The polymerization may be catalyzed by a catalyst, such as a
titanium-based catalyst (e.g., tetraisopropyltitanate, tetraisopropoxy
titanium, dibutoxydiacetoacetoxy titanium, or tetrabutyltitanate). If
desired, a diisocyanate chain extender may be reacted with the
copolyester to increase its molecular weight. Representative
diisocyanates may include toluene 2,4-diisocyanate, toluene
2,6-diisocyanate, 2,4'-diphenylmethane diisocyanate,
naphthylene-1,5-diisocyanate, xylylene diisocyanate, hexamethylene
diisocyanate ("HMDI"), isophorone diisocyanate and
methylenebis(2-isocyanatocyclohexane). Trifunctional isocyanate compounds
may also be employed that contain isocyanurate and/or biurea groups with
a functionality of not less than three, or to replace the diisocyanate
compounds partially by tri-or polyisocyanates. The preferred diisocyanate
is hexamethylene diisocyanate. The amount of the chain extender employed
is typically from about 0.3 to about 3.5 wt. %, in some embodiments, from
about 0.5 to about 2.5 wt. % based on the total weight percent of the
polymer.

[0021] The copolyesters may either be a linear polymer or a long-chain
branched polymer. Long-chain branched polymers are generally prepared by
using a low molecular weight branching agent, such as a polyol,
polycarboxylic acid, hydroxy acid, and so forth. Representative low
molecular weight polyols that may be employed as branching agents include
glycerol, trimethylolpropane, trimethylolethane, polyethertriols,
1,2,4-butanetriol, pentaerythritol, 1,2,6-hexanetriol, sorbitol,
1,1,4,4,-tetrakis(hydroxymethyl)cyclohexane, tris(2-hydroxyethyl)
isocyanurate, and dipentaerythritol. Representative higher molecular
weight polyols (molecular weight of 400 to 3000) that may be used as
branching agents include triols derived by condensing alkylene oxides
having 2 to 3 carbons, such as ethylene oxide and propylene oxide with
polyol initiators. Representative polycarboxylic acids that may be used
as branching agents include hemimellitic acid, trimellitic
(1,2,4-benzenetricarboxylic) acid and anhydride, trimesic
(1,3,5-benzenetricarboxylic) acid, pyromellitic acid and anhydride,
benzenetetracarboxylic acid, benzophenone tetracarboxylic acid,
1,1,2,2-ethane-tetracarboxylic acid, 1,1,2-ethanetricarboxylic acid,
1,3,5-pentanetricarboxylic acid, and 1,2,3,4-cyclopentanetetracarboxylic
acid. Representative hydroxy acids that may be used as branching agents
include malic acid, citric acid, tartaric acid, 3-hydroxyglutaric acid,
mucic acid, trihydroxyglutaric acid, 4-carboxyphthalic anhydride,
hydroxyisophthalic acid, and 4-(beta-hydroxyethyl)phthalic acid. Such
hydroxy acids contain a combination of 3 or more hydroxyl and carboxyl
groups. Especially preferred branching agents include trimellitic acid,
trimesic acid, pentaerythritol, trimethylol propane and
1,2,4-butanetriol.

[0022] The aromatic dicarboxylic acid monomer constituent may be present
in the copolyester in an amount of from about 10 mole % to about 40 mole
%, in some embodiments from about 15 mole % to about 35 mole %, and in
some embodiments, from about 15 mole % to about 30 mole %. The aliphatic
dicarboxylic acid monomer constituent may likewise be present in the
copolyester in an amount of from about 15 mole % to about 45 mole %, in
some embodiments from about 20 mole % to about 40 mole %, and in some
embodiments, from about 25 mole % to about 35 mole %. The polyol monomer
constituent may also be present in the aliphatic-aromatic copolyester in
an amount of from about 30 mole % to about 65 mole %, in some embodiments
from about 40 mole % to about 50 mole %, and in some embodiments, from
about 45 mole % to about 55 mole %.

[0023] In one particular embodiment, for example, the aliphatic-aromatic
copolyester may comprise the following structure:

##STR00001##

[0024] wherein,

[0025] m is an integer from 2 to 10, in some embodiments from 2 to 4, and
in one embodiment, 4;

[0026] n is an integer from 0 to 18, in some embodiments from 2 to 4, and
in one embodiment, 4;

[0027] p is an integer from 2 to 10, in some embodiments from 2 to 4, and
in one embodiment, 4;

[0028] x is an integer greater than 1; and

[0029] y is an integer greater than 1. One example of such a copolyester
is polybutylene adipate terephthalate, which is commercially available
under the designation ECOFLEX® F BX 7011 from BASF Corp. Another
example of a suitable copolyester containing an aromatic terephtalic acid
monomer constituent is available under the designation ENPOL® 8060M
from IRE Chemicals (South Korea). Other suitable aliphatic-aromatic
copolyesters may be described in U.S. Pat. Nos. 5,292,783; 5,446,079;
5,559,171; 5,580,911; 5,599,858; 5,817,721; 5,900,322; and 6,258,924,
which are incorporated herein in their entirety by reference thereto for
all purposes.

[0030] B. Starch

[0031] A starch is also employed in the present invention that is
water-sensitive in that it contains one or more starches that are
generally dispersible in water. Starch is a natural polymer composed of
amylose and amylopectin. Amylose is essentially a linear polymer having a
molecular weight in the range of 100,000-500,000, whereas amylopectin is
a highly branched polymer having a molecular weight of up to several
million. Although starch is produced in many plants, typical sources
includes seeds of cereal grains, such as corn, waxy corn, wheat, sorghum,
rice, and waxy rice; tubers, such as potatoes; roots, such as tapioca
(i.e., cassava and manioc), sweet potato, and arrowroot; and the pith of
the sago palm. Broadly speaking, any natural (unmodified) and/or modified
starch having the desired water sensitivity properties may be employed in
the present invention. Modified starches, for instance, are often
employed that have been chemically modified by typical processes known in
the art (e.g., esterification, etherification, oxidation, acid
hydrolysis, enzymatic hydrolysis, etc.). Starch ethers and/or esters may
be particularly desirable, such as hydroxyalkyl starches, carboxymethyl
starches, etc. The hydroxyalkyl group of hydroxylalkyl starches may
contain, for instance, 2 to 10 carbon atoms, in some embodiments from 2
to 6 carbon atoms, and in some embodiments, from 2 to 4 carbon atoms.
Representative hydroxyalkyl starches such as hydroxyethyl starch,
hydroxypropyl starch, hydroxybutyl starch, and derivatives thereof.
Starch esters, for instance, may be prepared using a wide variety of
anhydrides (e.g., acetic, propionic, butyric, and so forth), organic
acids, acid chlorides, or other esterification reagents. The degree of
esterification may vary as desired, such as from 1 to 3 ester groups per
glucosidic unit of the starch.

[0032] C. Water-Soluble Polymer

[0033] The film also includes one or more water-soluble polymers. Without
intending to be limited by theory, the present inventors believe that
such polymers may improve the compatibility between the starch and
biodegradable polyester, thereby leading to a film that exhibits
excellent mechanical and physical properties during use. Such polymers
may be formed from monomers such as vinyl pyrrolidone, hydroxyethyl
acrylate or methacrylate (e.g., 2-hydroxyethyl methacrylate),
hydroxypropyl acrylate or methacrylate, acrylic or methacrylic acid,
acrylic or methacrylic esters or vinyl pyridine, acrylamide, vinyl
acetate, vinyl alcohol, ethylene oxide, derivatives thereof, and so
forth. Other examples of suitable monomers are described in U.S. Pat. No.
4,499,154 to James, et al., which is incorporated herein in its entirety
by reference thereto for all purposes. The resulting polymers may be
homopolymers or interpolymers (e.g., copolymer, terpolymer, etc.), and
may be nonionic, anionic, cationic, or amphoteric. In addition, the
polymer may be of one type (i.e., homogeneous), or mixtures of different
polymers may be used (i.e., heterogeneous).

[0034] In one particular embodiment, the water-soluble polymer contains a
repeating unit having a functional hydroxyl group, such as polyvinyl
alcohol ("PVOH"), copolymers of polyvinyl alcohol (e.g., ethylene vinyl
alcohol copolymers, methyl methacrylate vinyl alcohol copolymers, etc.),
etc. Vinyl alcohol polymers, for instance, have at least two or more
vinyl alcohol units in the molecule and may be a homopolymer of vinyl
alcohol, or a copolymer containing other monomer units. Vinyl alcohol
homopolymers may be obtained by hydrolysis of a vinyl ester polymer, such
as vinyl formate, vinyl acetate, vinyl propionate, etc. Vinyl alcohol
copolymers may be obtained by hydrolysis of a copolymer of a vinyl ester
with an olefin having 2 to 30 carbon atoms, such as ethylene, propylene,
1-butene, etc.; an unsaturated carboxylic acid having 3 to 30 carbon
atoms, such as acrylic acid, methacrylic acid, crotonic acid, maleic
acid, fumaric acid, etc., or an ester, salt, anhydride or amide thereof;
an unsaturated nitrile having 3 to 30 carbon atoms, such as
acrylonitrile, methacrylonitrile, etc.; a vinyl ether having 3 to 30
carbon atoms, such as methyl vinyl ether, ethyl vinyl ether, etc.; and so
forth. The degree of hydrolysis may be selected to optimize solubility,
etc., of the polymer. For example, the degree of hydrolysis may be from
about 60 mole % to about 95 mole %, in some embodiments from about 80
mole % to about 90 mole %, and in some embodiments, from about 85 mole %
to about 89 mole %. Examples of suitable partially hydrolyzed polyvinyl
alcohol polymers are available under the designation CELVOL® 203, 205,
502, 504, 508, 513, 518, 523, 530, or 540 from Celanese Corp. Other
suitable partially hydrolyzed polyvinyl alcohol polymers are available
under the designation ELVANOL® 50-14, 50-26, 50-42, 51-03, 51-04,
51-05, 51-08, and 52-22 from DuPont.

[0035] D. Plasticizer

[0036] A plasticizer is also employed in the film to help render the
biodegradable polyester, starch, and/or water-soluble polymer
melt-processible. Starches, for instance, normally exist in the form of
granules that have a coating or outer membrane that encapsulates the more
water-soluble amylose and amylopectin chains within the interior of the
granule. When heated, plasticizers (e.g., polar solvents) may soften and
penetrate the outer membrane and cause the inner starch chains to absorb
water and swell. This swelling will, at some point, cause the outer shell
to rupture and result in an irreversible destructurization of the starch
granule. Once destructurized, the starch polymer chains containing
amylose and amylopectin polymers, which are initially compressed within
the granules, will stretch out and form a generally disordered
intermingling of polymer chains. Upon resolidification, however, the
chains may reorient themselves to form crystalline or amorphous solids
having varying strengths depending on the orientation of the starch
polymer chains. Because the starch (natural or modified) is thus capable
of melting and resolidifying, it is generally considered a "thermoplastic
starch."

[0038] The plasticizer may be incorporated into the film using any of a
variety of known techniques. For example, the starch and/or water-soluble
polymers may be "pre-plasticized" prior to incorporation into the film.
Alternatively, one or more of the components may be plasticized at the
same time as they are blended together. Regardless, batch and/or
continuous melt blending techniques may be employed to blend the
components. For example, a mixer/kneader, Banbury mixer, Farrel
continuous mixer, single-screw extruder, twin-screw extruder, roll mill,
etc., may be utilized. One particularly suitable melt-blending device is
a co-rotating, twin-screw extruder (e.g., USALAB twin-screw extruder
available from Thermo Electron Corporation of Stone, England or an
extruder available from Werner-Pfreiderer from Ramsey, N.J.). Such
extruders may include feeding and venting ports and provide high
intensity distributive and dispersive mixing. For example, a starch
composition may be initially fed to a feeding port of the twin-screw
extruder. Thereafter, a plasticizer may be injected into the starch
composition. Alternatively, the starch composition may be simultaneously
fed to the feed throat of the extruder or separately at a different point
along its length. Melt blending may occur at any of a variety of
temperatures, such as from about 30° C. to about 200° C.,
in some embodiments, from about 40° C. to about 160° C.,
and in some embodiments, from about 50° C. to about 150° C.

[0039] The amounts of the biodegradable polyester, starch, water-soluble
polymer, and plasticizer employed in the film are controlled in the
present invention to achieve a desirable balance between
biodegradability, mechanical strength, and water-sensitivity. For
example, biodegradable polyesters typically constitute from about 1 wt. %
to about 50 wt. %, in some embodiments from about 2 wt. % to about 40 wt.
%, and in some embodiments, from about 5 to about 35 wt. % of the film.
Water-soluble polymers may constitute from about 0.1 wt. % to about 40
wt. %, in some embodiments from about 1 wt. % to about 35 wt. %, and in
some embodiments, from about 5 to about 30 wt. % of the film.
Plasticizers may constitute from about 0.1 wt. % to about 40 wt. %, in
some embodiments from about 1 wt. % to about 35 wt. %, and in some
embodiments, from about 5 to about 30 wt. % of the film. Further,
starches may constitute from about 0.5 wt. % to about 45 wt. %, in some
embodiments from about 5 wt. % to about 35 wt. %, and in some
embodiments, from about 10 to about 30 wt. % of the film. It should be
understood that the weight of starch referenced herein includes any bound
water that naturally occurs in the starch before mixing it with other
components. Starches, for instance, typically have a bound water content
of about 5% to 16% by weight of the starch.

[0040] E. Other Components

[0041] In addition to the components noted above, other additives may also
be incorporated into the film of the present invention, such as
dispersion aids, melt stabilizers, processing stabilizers, heat
stabilizers, light stabilizers, antioxidants, heat aging stabilizers,
whitening agents, antiblocking agents, bonding agents, lubricants,
fillers, etc. Dispersion aids, for instance, may also be employed to help
create a uniform dispersion of the starch/polyvinyl alcohol/plasticizer
mixture and retard or prevent separation into constituent phases.
Likewise, the dispersion aids may also improve the water dispersibility
of the film. When employed, the dispersion aid(s) typically constitute
from about 0.01 wt. % to about 15 wt. %, in some embodiments from about
0.1 wt. % to about 10 wt. %, and in some embodiments, from about 0.5 wt.
% to about 5 wt. % of the film. Although any dispersion aid may generally
be employed in the present invention, surfactants having a certain
hydrophilic/lipophilic balance ("HLB") may improve the long-term
stability of the composition. The HLB index is well known in the art and
is a scale that measures the balance between the hydrophilic and
lipophilic solution tendencies of a compound. The HLB scale ranges from 1
to approximately 50, with the lower numbers representing highly
lipophilic tendencies and the higher numbers representing highly
hydrophilic tendencies. In some embodiments of the present invention, the
HLB value of the surfactants is from about 1 to about 20, in some
embodiments from about 1 to about 15 and in some embodiments, from about
2 to about 10. If desired, two or more surfactants may be employed that
have HLB values either below or above the desired value, but together
have an average HLB value within the desired range.

[0042] One particularly suitable class of surfactants for use in the
present invention are nonionic surfactants, which typically have a
hydrophobic base (e.g., long chain alkyl group or an alkylated aryl
group) and a hydrophilic chain (e.g., chain containing ethoxy and/or
propoxy moieties). For instance, some suitable nonionic surfactants that
may be used include, but are not limited to, ethoxylated alkylphenols,
ethoxylated and propoxylated fatty alcohols, polyethylene glycol ethers
of methyl glucose, polyethylene glycol ethers of sorbitol, ethylene
oxide-propylene oxide block copolymers, ethoxylated esters of fatty
(C8-C18) acids, condensation products of ethylene oxide with
long chain amines or amides, condensation products of ethylene oxide with
alcohols, fatty acid esters, monoglyceride or diglycerides of long chain
alcohols, and mixtures thereof. In one particular embodiment, the
nonionic surfactant may be a fatty acid ester, such as a sucrose fatty
acid ester, glycerol fatty acid ester, propylene glycol fatty acid ester,
sorbitan fatty acid ester, pentaerythritol fatty acid ester, sorbitol
fatty acid ester, and so forth. The fatty acid used to form such esters
may be saturated or unsaturated, substituted or unsubstituted, and may
contain from 6 to 22 carbon atoms, in some embodiments from 8 to 18
carbon atoms, and in some embodiments, from 12 to 14 carbon atoms. In one
particular embodiment, mono- and di-glycerides of fatty acids may be
employed in the present invention.

[0043] Fillers may also be employed in the present invention. Fillers are
particulates or other forms of material that may be added to the film
polymer extrusion blend and that will not chemically interfere with the
extruded film, but which may be uniformly dispersed throughout the film.
Fillers may serve a variety of purposes, including enhancing film opacity
and/or breathability (i.e., vapor-permeable and substantially
liquid-impermeable). For instance, filled films may be made breathable by
stretching, which causes the polymer to break away from the filler and
create microporous passageways. Breathable microporous elastic films are
described, for example, in U.S. Pat. Nos. 5,997,981; 6,015,764; and
6,111,163 to McCormack, et al.; 5,932,497 to Morman, et al.; 6,461,457 to
Taylor, et al., which are incorporated herein in their entirety by
reference thereto for all purposes. Further, hindered phenols are
commonly used as an antioxidant in the production of films. Some suitable
hindered phenols include those available from Ciba Specialty Chemicals
under the trade name "Irganox®", such as Irganox® 1076, 1010, or
E 201. Moreover, bonding agents may also be added to the film to
facilitate bonding of the film to additional materials (e.g., nonwoven
webs). Examples of such bonding agents include hydrogenated hydrocarbon
resins. Other suitable bonding agents are described in U.S. Pat. Nos.
4,789,699 to Kieffer et al. and 5,695,868 to McCormack, which are
incorporated herein in their entirety by reference thereto for all
purposes.

II. Film Construction

[0044] The film of the present invention may be mono- or multi-layered.
Multilayer films may be prepared by co-extrusion of the layers, extrusion
coating, or by any conventional layering process. Such multilayer films
normally contain at least one base layer and at least one skin layer, but
may contain any number of layers desired. For example, the multilayer
film may be formed from a base layer and one or more skin layers, wherein
the base layer is formed from a blend of the biodegradable polyester,
starch, water-soluble polymer, and plasticizer. In most embodiments, the
skin layer(s) are formed from a biodegradable polyester, thermoplastic
starch, water-soluble polymer, and plasticizer as described above. It
should be understood, however, that other polymers may also be employed
in the skin layer(s), such as polyolefin polymers (e.g., linear
low-density polyethylene (LLDPE) or polypropylene). The term "linear low
density polyethylene" refers to polymers of ethylene and higher alpha
olefin comonomers, such as C3-C12 and combinations thereof,
having a Melt Index (as measured by ASTM D-1238) of from about 0.5 to
about 30 grams per 10 minutes at 190° C. Examples of predominately
linear polyolefin polymers include, without limitation, polymers produced
from the following monomers: ethylene, propylene, 1-butene,
4-methyl-pentene, 1-hexene, 1-octene and higher olefins as well as
copolymers and terpolymers of the foregoing. In addition, copolymers of
ethylene and other olefins including butene, 4-methyl-pentene, hexene,
heptene, octene, decene, etc., are also examples of predominately linear
polyolefin polymers. Additional film-forming polymers that may be
suitable for use with the present invention, alone or in combination with
other polymers, include ethylene vinyl acetate, ethylene ethyl acrylate,
ethylene acrylic acid, ethylene methyl acrylate, ethylene normal butyl
acrylate, nylon, ethylene vinyl alcohol, polystyrene, polyurethane, and
so forth.

[0045] Any known technique may be used to form a film from the compounded
material, including blowing, casting, flat die extruding, etc. In one
particular embodiment, the film may be formed by a blown process in which
a gas (e.g., air) is used to expand a bubble of the extruded polymer
blend through an annular die.

[0046] The bubble is then collapsed and collected in flat film form.
Processes for producing blown films are described, for instance, in U.S.
Pat. Nos. 3,354,506 to Raley; 3,650,649 to Schippers; and 3,801,429 to
Schrenk et al., as well as U.S. Patent Application Publication Nos.
2005/0245162 to McCormack, et al. and 2003/0068951 to Boggs, et al., all
of which are incorporated herein in their entirety by reference thereto
for all purposes. In yet another embodiment, however, the film is formed
using a casting technique.

[0047] Referring to FIG. 1, for instance, one embodiment of a method for
forming a cast film is shown. The raw materials (e.g., biodegradable
polyester, starch, water-soluble polymer, plasticizer, etc.) may be
supplied to a melt blending device, either separately or as a blend. In
one embodiment, for example, a starch, water-soluble polymer,
plasticizer, and/or biodegradable polyester are separately supplied to a
melt blending device where they are dispersively blended in a manner such
as described above. For example, an extruder may be employed that
includes feeding and venting ports. In one embodiment, the biodegradable
polyester may be fed to a feeding port of the twin-screw extruder and
melted. Thereafter, the starch, plasticizer, and water-soluble polymer
may be fed into the polymer melt. Regardless, the materials are blended
under high shear/pressure and heat to ensure sufficient mixing. For
example, melt blending may occur at a temperature of from about
50° C. to about 300° C., in some embodiments, from about
70° C. to about 250° C., and in some embodiments, from
about 90° C. to about 180° C. Likewise, the apparent shear
rate during melt blending may range from about 100 seconds-1 to
about 10,000 seconds-1, in some embodiments from about 500
seconds-1 to about 5000 seconds-1, and in some embodiments,
from about 800 seconds-1 to about 1200 seconds-1. The apparent
shear rate is equal to 4Q/πR3, where Q is the volumetric flow
rate ("m3/s") of the polymer melt and R is the radius ("m") of the
capillary (e.g., extruder die) through which the melted polymer flows.

[0048] Thereafter, the extruded material may be immediately chilled and
cut into pellet form. In the particular embodiment of FIG. 1, the
compounded material (not shown) is then supplied to an extrusion
apparatus 80 and cast onto a casting roll 90 to form a single-layered
precursor film 10a. If a multilayered film is to be produced, the
multiple layers are co-extruded together onto the casting roll 90. The
casting roll 90 may optionally be provided with embossing elements to
impart a pattern to the film. Typically, the casting roll 90 is kept at
temperature sufficient to solidify and quench the sheet 10a as it is
formed, such as from about 20 to 60° C. If desired, a vacuum box
may be positioned adjacent to the casting roll 90 to help keep the
precursor film 10a close to the surface of the roll 90. Additionally, air
knives or electrostatic pinners may help force the precursor film 10a
against the surface of the casting roll 90 as it moves around a spinning
roll. An air knife is a device known in the art that focuses a stream of
air at a very high flow rate to pin the edges of the film.

[0049] Once cast, the film 10a may then be optionally oriented in one or
more directions to further improve film uniformity and reduce thickness.
Orientation may also form micropores in a film containing a filler, thus
providing breathability to the film. For example, the film may be
immediately reheated to a temperature below the melting point of one or
more polymers in the film, but high enough to enable the composition to
be drawn or stretched. In the case of sequential orientation, the
"softened" film is drawn by rolls rotating at different speeds of
rotation such that the sheet is stretched to the desired draw ratio in
the longitudinal direction (machine direction). This "uniaxially"
oriented film may then be laminated to a fibrous web. In addition, the
uniaxially oriented film may also be oriented in the cross-machine
direction to form a "biaxially oriented" film. For example, the film may
be clamped at its lateral edges by chain clips and conveyed into a tenter
oven. In the tenter oven, the film may be reheated and drawn in the
cross-machine direction to the desired draw ratio by chain clips diverged
in their forward travel.

[0050] Referring again to FIG. 1, for instance, one method for forming a
uniaxially oriented film is shown. As illustrated, the precursor film 10a
is directed to a film-orientation unit 100 or machine direction orienter
("MDO"), such as commercially available from Marshall and Willams, Co. of
Providence, R.I. The MDO has a plurality of stretching rolls (such as
from 5 to 8) which progressively stretch and thin the film in the machine
direction, which is the direction of travel of the film through the
process as shown in FIG. 1. While the MDO 100 is illustrated with eight
rolls, it should be understood that the number of rolls may be higher or
lower, depending on the level of stretch that is desired and the degrees
of stretching between each roll. The film may be stretched in either
single or multiple discrete stretching operations. It should be noted
that some of the rolls in an MDO apparatus may not be operating at
progressively higher speeds. If desired, some of the rolls of the MDO 100
may act as preheat rolls. If present, these first few rolls heat the film
10a above room temperature (e.g., to 125° F.). The progressively
faster speeds of adjacent rolls in the MDO act to stretch the film 10a.
The rate at which the stretch rolls rotate determines the amount of
stretch in the film and final film weight.

[0051] The resulting film 10b may then be wound and stored on a take-up
roll 60. While not shown here, various additional potential processing
and/or finishing steps known in the art, such as slitting, treating,
aperturing, printing graphics, or lamination of the film with other
layers (e.g., nonwoven web materials), may be performed without departing
from the spirit and scope of the invention.

[0052] The thickness of the resulting water-sensitive biodegradable film
may generally vary depending upon the desired use. Nevertheless, the film
thickness is typically minimized to reduce the time needed for the film
to disperse in water. Thus, in most embodiments of the present invention,
the water-sensitive biodegradable film has a thickness of about 50
micrometers or less, in some embodiments from about 1 to about 40
micrometers, in some embodiments from about 2 to about 35 micrometers,
and in some embodiments, from about 5 to about 30 micrometers.

[0053] Despite having such a small thickness and good sensitivity in
water, the film of the present invention is nevertheless able to retain
good dry mechanical properties during use. One parameter that is
indicative of the relative dry strength of the film is the ultimate
tensile strength, which is equal to the peak stress obtained in a
stress-strain curve. Desirably, the film of the present invention
exhibits an ultimate tensile strength in the machine direction ("MD") of
from about 10 to about 80 Megapascals (MPa), in some embodiments from
about 15 to about 60 MPa, and in some embodiments, from about 20 to about
50 MPa, and an ultimate tensile strength in the cross-machine direction
("CD") of from about 2 to about 40 Megapascals (MPa), in some embodiments
from about 4 to about 40 MPa, and in some embodiments, from about 5 to
about 30 MPa. Although possessing good strength, it is also desirable
that the film is not too stiff. One parameter that is indicative of the
relative stiffness of the film (when dry) is Young's modulus of
elasticity, which is equal to the ratio of the tensile stress to the
tensile strain and is determined from the slope of a stress-strain curve.
For example, the film typically exhibits a Young's modulus in the machine
direction ("MD") of from about 50 to about 1200 Megapascals ("MPa"), in
some embodiments from about 200 to about 1000 MPa, and in some
embodiments, from about 400 to about 800 MPa, and a Young's modulus in
the cross-machine direction ("CD") of from about 50 to about 1000
Megapascals ("MPa"), in some embodiments from about 100 to about 800 MPa,
and in some embodiments, from about 150 to about 500 MPa. The MD and CD
elongation of the film may also be about 50% or more, in some embodiments
about 100% or more, and in some embodiments, about 150% or more.

[0054] The water-sensitive biodegradable film of the present invention may
be used in a wide variety of applications. For example, as indicated
above, the film may be used in an absorbent article. An "absorbent
article" generally refers to any article capable of absorbing water or
other fluids. Examples of some absorbent articles include, but are not
limited to, personal care absorbent articles, such as diapers, training
pants, absorbent underpants, incontinence articles, feminine hygiene
products (e.g., sanitary napkins, pantiliners, etc.), swim wear, baby
wipes, and so forth; medical absorbent articles, such as garments,
fenestration materials, underpads, bedpads, bandages, absorbent drapes,
and medical wipes; food service wipers; clothing articles; and so forth.
Several examples of such absorbent articles are described in U.S. Pat.
Nos. 5,649,916 to DiPalma, et al.; 6,110,158 to Kielpikowski; 6,663,611
to Blaney, et al., which are incorporated herein in their entirety by
reference thereto for all purposes. Still other suitable articles are
described in U.S. Patent Application Publication No. 2004/0060112 A1 to
Fell et al., as well as U.S. Pat. Nos. 4,886,512 to Damico et al.;
5,558,659 to Sherrod et al.; 6,888,044 to Fell et al.; and 6,511,465 to
Freiburger et al., all of which are incorporated herein in their entirety
by reference thereto for all purposes. Materials and processes suitable
for forming such absorbent articles are well known to those skilled in
the art.

[0055] As is well known in the art, the absorbent article may be provided
with adhesives (e.g., pressure-sensitive adhesives) that help removably
secure the article to the crotch portion of an undergarment and/or wrap
up the article for disposal. Suitable pressure-sensitive adhesives, for
instance, may include acrylic adhesives, natural rubber adhesives,
tackified block copolymer adhesives, polyvinyl acetate adhesives,
ethylene vinyl acetate adhesives, silicone adhesives, polyurethane
adhesives, thermosettable pressure-sensitive adhesives, such as epoxy
acrylate or epoxy polyester pressure-sensitive adhesives, etc. Such
pressure-sensitive adhesives are known in the art and are described in
the Handbook of Pressure Sensitive Adhesive Technology, Satas (Donatas),
1989, 2nd edition, Van Nostrand Reinhold. The pressure sensitive
adhesives may also include additives such as cross-linking agents,
fillers, gases, blowing agents, glass or polymeric microspheres, silica,
calcium carbonate fibers, surfactants, and so forth. The additives are
included in amounts sufficient to affect the desired properties.

[0056] The location of the adhesive on the absorbent article is not
critical and may vary widely depending on the intended use of the
article. For example, certain feminine hygiene products (e.g., sanitary
napkins) may have wings or flaps that laterally from a central absorbent
core and are intended to be folded around the edges of the wearer's
panties in the crotch region. The flaps may be provided with an adhesive
(e.g., pressure-sensitive adhesive) for affixing the flaps to the
underside of the wearer's panties.

[0057] Regardless of the particular location of the adhesive, however, a
release liner may be employed to cover the adhesive, thereby protecting
it from dirt, drying out, and premature sticking prior to use. The
release liner may contain a release coating that enhances the ability of
the liner to be peeled from an adhesive. The release coating contains a
release agent, such as a hydrophobic polymer.

[0058] Exemplary hydrophobic polymers include, for instance, silicones
(e.g., polysiloxanes, epoxy silicones, etc.), perfluoroethers,
fluorocarbons, polyurethanes, and so forth. Examples of such release
agents are described, for instance, in U.S. Pat. Nos. 6,530,910 to
Pomplun, et al.; 5,985,396 to Kerins, et al.; and 5,981,012 to Pomplun,
et al., which are incorporated herein in their entirety by reference
thereto for all purposes. One particularly suitable release agent is an
amorphous polyolefin having a melt viscosity of about 400 to about 10,000
cps at 190° C., such as made by the U.S. Rexene Company under the
tradename REXTAC® (e.g., RT2315, RT2535 and RT2330). The release
coating may also contain a detackifier, such as a low molecular weight,
highly branched polyolefin. A particularly suitable low molecular weight,
highly branched polyolefin is VYBAR® 253, which is made by the
Petrolite Corporation. Other additives may also be employed in the
release coating, such as compatibilizers, processing aids, plasticizers,
tackifiers, slip agents, and antimicrobial agents, and so forth. The
release coating may be applied to one or both surfaces of the liner, and
may cover all or only a portion of a surface. Any suitable technique may
be employed to apply the release coating, such as solvent-based coating,
hot melt coating, solventless coating, etc. Solvent-based coatings are
typically applied to the release liner by processes such as roll coating,
knife coating, curtain coating, gravure coating, wound rod coating, and
so forth. The solvent (e.g., water) is then removed by drying in an oven,
and the coating is optionally cured in the oven. Solventless coatings may
include solid compositions, such as silicones or epoxy silicones, which
are coated onto the liner and then cured by exposure to ultraviolet
light. Optional steps include priming the liner before coating or surface
modification of the liner, such as with corona treatment. Hot melt
coatings, such as polyethylenes or perfluoroethers, may be heated and
then applied through a die or with a heated knife. Hot melt coatings may
be applied by co-extruding the release agent with the release liner in
blown film or sheet extruder for ease of coating and for process
efficiency.

[0059] To facilitate its ability to be easily disposed, the release liner
may be formed from a water-sensitive biodegradable film in accordance
with the present invention. In this regard, one particular embodiment of
a sanitary napkin that may employ the water-sensitive biodegradable film
of the present invention will now be described in more detail. For
purposes of illustration only, an absorbent article 20 is shown in FIG. 2
as a sanitary napkin for feminine hygiene. In the illustrated embodiment,
the absorbent article 20 includes a main body portion 22 containing a
topsheet 40, an outer cover or backsheet 42, an absorbent core 44
positioned between the backsheet 42 and the topsheet 40, and a pair of
flaps 24 extending from each longitudinal side 22a of the main body
portion 22. The topsheet 40 defines a bodyfacing surface of the absorbent
article 20. The absorbent core 44 is positioned inward from the outer
periphery of the absorbent article 20 and includes a body-facing side
positioned adjacent the topsheet 40 and a garment-facing surface
positioned adjacent the backsheet 42.

[0060] The topsheet 40 is generally designed to contact the body of the
user and is liquid-permeable. The topsheet 40 may surround the absorbent
core 44 so that it completely encases the absorbent article 20.
Alternatively, the topsheet 40 and the backsheet 42 may extend beyond the
absorbent core 44 and be peripherally joined together, either entirely or
partially, using known techniques. Typically, the topsheet 40 and the
backsheet 42 are joined by adhesive bonding, ultrasonic bonding, or any
other suitable joining method known in the art. The topsheet 40 is
sanitary, clean in appearance, and somewhat opaque to hide bodily
discharges collected in and absorbed by the absorbent core 44. The
topsheet 40 further exhibits good strike-through and rewet
characteristics permitting bodily discharges to rapidly penetrate through
the topsheet 40 to the absorbent core 44, but not allow the body fluid to
flow back through the topsheet 40 to the skin of the wearer. For example,
some suitable materials that may be used for the topsheet 40 include
nonwoven materials, perforated thermoplastic films, or combinations
thereof. A nonwoven fabric made from polyester, polyethylene,
polypropylene, bicomponent, nylon, rayon, or like fibers may be utilized.
For instance, a white uniform spunbond material is particularly desirable
because the color exhibits good masking properties to hide menses that
has passed through it. U.S. Pat. No. 4,801,494 to Datta, et al. and U.S.
Pat. No. 4,908,026 to Sukiennik, et al. teach various other cover
materials that may be used in the present invention.

[0061] The topsheet 40 may also contain a plurality of apertures (not
shown) formed therethrough to permit body fluid to pass more readily into
the absorbent core 44. The apertures may be randomly or uniformly
arranged throughout the topsheet 40, or they may be located only in the
narrow longitudinal band or strip arranged along the longitudinal axis
X-X of the absorbent article 20. The apertures permit rapid penetration
of body fluid down into the absorbent core 44. The size, shape, diameter
and number of apertures may be varied to suit one's particular needs.

[0062] As stated above, the absorbent article also includes a backsheet
42. The backsheet 42 is generally liquid-impermeable and designed to face
the inner surface, i.e., the crotch portion of an undergarment (not
shown). The backsheet 42 may permit a passage of air or vapor out of the
absorbent article 20, while still blocking the passage of liquids. Any
liquid-impermeable material may generally be utilized to form the
backsheet 42. For example, one suitable material that may be utilized is
a microembossed polymeric film, such as polyethylene or polypropylene. In
particular embodiments, a polyethylene film is utilized that has a
thickness in the range of about 0.2 mils to about 5.0 mils, and
particularly between about 0.5 to about 3.0 mils.

[0063] The absorbent article 20 also contains an absorbent core 44
positioned between the topsheet 40 and the backsheet 42. The absorbent
core 44 may be formed from a single absorbent member or a composite
containing separate and distinct absorbent members. It should be
understood, however, that any number of absorbent members may be utilized
in the present invention. For example, in one embodiment, the absorbent
core 44 may contain an intake member (not shown) positioned between the
topsheet 40 and a transfer delay member (not shown). The intake member
may be made of a material that is capable of rapidly transferring, in the
z-direction, body fluid that is delivered to the topsheet 40. The intake
member may generally have any shape and/or size desired. In one
embodiment, the intake member has a rectangular shape, with a length
equal to or less than the overall length of the absorbent article 20, and
a width less than the width of the absorbent article 20. For example, a
length of between about 150 mm to about 300 mm and a width of between
about 10 mm to about 60 mm may be utilized.

[0064] Any of a variety of different materials may be used for the intake
member to accomplish the above-mentioned functions. The material may be
synthetic, cellulosic, or a combination of synthetic and cellulosic
materials. For example, airlaid cellulosic tissues may be suitable for
use in the intake member. The airlaid cellulosic tissue may have a basis
weight ranging from about 10 grams per square meter (gsm) to about 300
gsm, and in some embodiments, between about 100 gsm to about 250 gsm. In
one embodiment, the airlaid cellulosic tissue has a basis weight of about
200 gsm. The airlaid tissue may be formed from hardwood and/or softwood
fibers. The airlaid tissue has a fine pore structure and provides an
excellent wicking capacity, especially for menses.

[0065] If desired, a transfer delay member (not shown) may be positioned
vertically below the intake member. The transfer delay member may contain
a material that is less hydrophilic than the other absorbent members, and
may generally be characterized as being substantially hydrophobic. For
example, the transfer delay member may be a nonwoven fibrous web composed
of a relatively hydrophobic material, such as polypropylene,
polyethylene, polyester or the like, and also may be composed of a blend
of such materials. One example of a material suitable for the transfer
delay member is a spunbond web composed of polypropylene, multi-lobal
fibers. Further examples of suitable transfer delay member materials
include spunbond webs composed of polypropylene fibers, which may be
round, tri-lobal or poly-lobal in cross-sectional shape and which may be
hollow or solid in structure. Typically the webs are bonded, such as by
thermal bonding, over about 3% to about 30% of the web area. Other
examples of suitable materials that may be used for the transfer delay
member are described in U.S. Pat. No. 4,798,603 to Meyer, et al. and U.S.
Pat. No. 5,248,309 to Serbiak, et al., which are incorporated herein in
their entirety by reference thereto for all purposes. To adjust the
performance of the invention, the transfer delay member may also be
treated with a selected amount of surfactant to increase its initial
wettability.

[0066] The transfer delay member may generally have any size, such as a
length of about 150 mm to about 300 mm. Typically, the length of the
transfer delay member is approximately equal to the length of the
absorbent article 20. The transfer delay member may also be equal in
width to the intake member, but is typically wider. For example, the
width of the transfer delay member may be from between about 50 mm to
about 75 mm, and particularly about 48 mm. The transfer delay member
typically has a basis weight less than that of the other absorbent
members. For example, the basis weight of the transfer delay member is
typically less than about 150 grams per square meter (gsm), and in some
embodiments, between about 10 gsm to about 100 gsm. In one particular
embodiment, the transfer delay member is formed from a spunbonded web
having a basis weight of about 30 gsm.

[0067] Besides the above-mentioned members, the absorbent core 44 may also
include a composite absorbent member (not shown), such as a coform
material. In this instance, fluids may be wicked from the transfer delay
member into the composite absorbent member. The composite absorbent
member may be formed separately from the intake member and/or transfer
delay member, or may be formed simultaneously therewith. In one
embodiment, for example, the composite absorbent member may be formed on
the transfer delay member or intake member, which acts a carrier during
the coform process described above.

[0068] Regardless of its particular construction, the absorbent article 20
typically contains an adhesive for securing to an undergarment. An
adhesive may be provided at any location of the absorbent article 20,
such as on the lower surface of the backsheet 42. In this particular
embodiment, the backsheet 42 carries a longitudinally central strip of
garment adhesive 54 covered before use by a peelable release liner 58,
which may be formed in accordance with the present invention. Each of the
flaps 24 may also contain an adhesive 56 positioned adjacent to the
distal edge 34 of the flap 24. A peelable release liner 57, which may
also be formed in accordance with the present invention, may cover the
adhesive 56 before use. Thus, when a user of the sanitary absorbent
article 20 wishes to expose the adhesives 54 and 56 and secure the
absorbent article 20 to the underside of an undergarment, the user simply
peels away the liners 57 and 58 and disposed them in a water-based
disposal system (e.g., in a toilet).

[0069] Although various configurations of a release liner have been
described above, it should be understood that other release liner
configurations are also included within the scope of the present
invention. Further, the present invention is by no means limited to
release liners and the water-sensitive biodegradable film may be
incorporated into a variety of different components of an absorbent
article. For example, referring again to FIG. 2, the backsheet 42 of the
napkin 20 may include the water-sensitive film of the present invention.
In such embodiments, the film may be used alone to form the backsheet 42
or laminated to one or more additional materials, such as a nonwoven web.
The water-sensitive biodegradable film of the present invention may also
be used in applications other than absorbent articles. For example, the
film may be employed as an individual wrap, packaging pouch, or bag for
the disposal of a variety of articles, such as food products, absorbent
articles, etc. Various suitable pouch, wrap, or bag configurations for
absorbent articles are disclosed, for instance, in U.S. Pat. Nos.
6,716,203 to Sorebo, et al. and 6,380,445 to Moder, et al., as well as
U.S. Patent Application Publication No. 2003/0116462 to Sorebo, et al.,
all of which are incorporated herein in their entirety by reference
thereto for all purposes.

[0070] The present invention may be better understood with reference to
the following examples.

Test Methods

[0071] Tensile Properties:

[0072] The strip tensile strength values were determined in substantial
accordance with ASTM Standard D-5034. A constant-rate-of-extension type
of tensile tester was employed. The tensile testing system was a Sintech
1/D tensile tester, which is available from Sintech Corp. of Cary, N.C.
The tensile tester was equipped with TESTWORKS 4.08B software from MTS
Corporation to support the testing. An appropriate load cell was selected
so that the tested value fell within the range of 10-90% of the full
scale load. The film samples were initially cut into dog-bone shapes with
a center width of 3.0 mm before testing. The samples were held between
grips having a front and back face measuring 25.4 millimeters×76
millimeters. The grip faces were rubberized, and the longer dimension of
the grip was perpendicular to the direction of pull. The grip pressure
was pneumatically maintained at a pressure of 40 pounds per square inch.
The tensile test was run using a gauge length of 18.0 millimeters and a
break sensitivity of 40%. Five samples were tested by applying the test
load along the machine-direction and five samples were tested by applying
the test load along the cross direction. During the test, samples were
stretched at a crosshead speed of abut 127 millimeters per minute until
breakage occurred. The modulus, peak stress, peak strain (i.e., % strain
at peak load), and elongation were measured.

[0073] Water Disintegration Test:

[0074] The rate of film disintegration in tap water was tested using a
"slosh box", which has a physical dimension of a
14''×18''×12'' high plastic box on a hinged platform. One end
of the platform is attached to the reciprocating cam. The typical
amplitude is ±2'' (4'' range), with sloshing occurring at
0.5˜1.5 sloshes per second. The preferred action is 0.9˜1.3
sloshes per second. During a test, the slosh box rocks up and down with
the water inside, "sloshing" back and forth. This action produces a wave
front and intermittent motion on a sample susceptible to dispersing in
water. To quantify a measurement of sample film disintegration in water,
without image analysis, simply timing is sufficient. Three liters of tap
water were added into the slosh box and resulted in ˜5.5'' water
depth in the box. A frequency of 3.5 was selected for the testing. Each
film sample was cut into 1''×3'' size. Three pieces were dropped
into the slosh box. The time to disintegrate the sample under the defined
conditions was recorded twice for each sample. The average of the time to
the sample disintegration is then reported. Generally, films reach an
acceptable dispersion point when no piece is larger than 25 mm2 in
size within 6 hours of agitation.

Example 1

[0075] A thermoplastic hydroxypropylated starch was formed as follows.
Initially, a mixture of a hydroxypropylated starch (Glucosol 800,
manufactured by Chemstar Products Company, Minneapolis, Minn.),
surfactant (Excel P-40S, Kao Corporation, Tokyo, Japan), and plasticizer
(sorbitol) was made at a ratio of the 66 parts of starch, 4 parts of
surfactant, and 30 parts of plasticizer. A Hobart mixer was used for
mixing. The mixture was then added to a K-Tron feeder (K-Tron America,
Pitman, N.J.) that fed the material into a co-rotating, twin-screw
extruder (ZSK-30, diameter of 30 mm) that was manufactured by Werner and
Pfleiderer Corporation of Ramsey, N.J. The screw length was 1328
millimeters. The extruder had 14 barrels, numbered consecutively 1-14
from the feed hopper to the die. The first barrel #1 received the mixture
at 19 lbs/hr when the extruder was heated to a temperature for zones 1 to
7 of 100° C., 110° C., 124° C., 124° C.,
124° C., 110° C., and 105° C., respectively. The
screw speed was set at 160 rpm to achieve a melt pressure of 400-500 psi
and a torque of 50-60%. In some cases, a vent was also opened to release
steam generated due to the presence of the added water in the plasticizer
and inherent moisture in the starch. The strands cooled down through a
cooling belt (Minarik Electric Company, Glendale, Calif.). A pelletizer
(Conair, Bay City, Mich.) was used to cut the strands to produce
thermoplastic starch pellets, which were then collected and sealed in a
bag.

Example 2

[0076] A plasticized polyvinyl alcohol was formed as follows. Initially, a
mixture of a polyvinyl alcohol (Elvanol 51-05, a granular polymer having
a degree of hydrolysis of 87.0-89.0 mole % and manufactured by DuPont)
and plasticizer (sorbitol) was made at a ratio of the 80 parts polyvinyl
alcohol and 20 parts of plasticizer. A Hobart mixer was used for mixing.
The mixture was then added to a K-Tron feeder (K-Tron America, Pitman,
N.J.) that fed the material into a ZSK-30 co-rotating, twin-screw
extruder as described above. The first barrel #1 received the mixture at
25 lbs/hr when the extruder was heated to a temperature for zones 1 to 7
of 150° C., 160° C., 185° C., 190° C.,
190° C., 170° C., and 110° C., respectively. The
screw speed was set at 160 rpm to achieve a melt pressure of 280-300 psi
and a torque of 34-40%. In some cases, a vent was also opened release
steam generated due to the presence of the added water in the plasticizer
and inherent moisture in the starch. The strands cooled down through a
cooling belt (Minarik Electric Company, Glendale, Calif.). A pelletizer
(Conair, Bay City, Mich.) was used to cut the strands to produce
polyvinyl alcohol pellets, which were then collected and sealed in a bag.

Example 3

[0077] A plasticized polyvinyl alcohol was formed as follows. Initially, a
mixture of a polyvinyl alcohol (Celvol 203, a polymer having a degree of
hydrolysis of 87.0-89.0 mole % and manufactured by Celanese Chemicals)
and plasticizer (sorbitol) was made at a ratio of the 80 parts polyvinyl
alcohol and 20 parts of plasticizer. A Hobart mixer was used for mixing.
The mixture was then added to a K-Tron feeder (K-Trop America, Pitman,
N.J.) that fed the material into a ZSK-30 co-rotating, twin-screw
extruder as described above. The first barrel #1 received the mixture at
25 lbs/hr when the extruder was heated to a temperature for zones 1 to 7
of 150° C., 160° C., 185° C., 190° C.,
190° C., 170° C., and 110° C., respectively. The
screw speed was set at 160 rpm to achieve a melt pressure of 280-300 psi
and a torque of 34-40%. In some cases, a vent was also opened release
steam generated due to the presence of the added water in the plasticizer
and inherent moisture in the starch. The strands cooled down through a
cooling belt (Minarik Electric Company, Glendale, Calif.). A pelletizer
(Conair, Bay City, Mich.) was used to cut the strands to produce
polyvinyl alcohol pellets, which were then collected and sealed in a bag.

Example 4

[0078] A blend of hydroxypropylated starch and polyvinyl alcohol was
formed as follows. Initially, a mixture of a hydroxypropylated starch
(Glucosol 800), surfactant (Excel P-40S), plasticizer (sorbitol), and
polyvinyl alcohol (Elvanol 51-05) was made at a ratio of the 36 parts of
starch, 30 parts polyvinyl alcohol, 4 parts of surfactant, and 30 parts
of plasticizer. A Hobart mixer was used for mixing. The mixture was then
added to a K-Tron feeder (K-Tron America, Pitman, N.J.) that fed the
material into a ZSK-30 co-rotating, twin-screw extruder as described
above. The first barrel #1 received the mixture at 20 lbs/hr when the
extruder was heated to a temperature for zones 1 to 7 of 95° C.,
125° C., 140° C., 150° C., 150° C.,
145° C., and 130° C., respectively. The screw speed was set
at 150-160 rpm to achieve a melt pressure of 530-550 psi and a torque of
80-90%. In some cases, a vent was also opened release steam generated due
to the presence of the added water in the plasticizer and inherent
moisture in the starch. The strands cooled down through a cooling belt
(Minarik Electric Company, Glendale, Calif.). A pelletizer (Conair, Bay
City, Mich.) was used to cut the strands to produce pellets, which were
then collected and sealed in a bag.

Example 5

[0079] A blend of starch and polyvinyl alcohol was formed as follows.
Initially, a mixture of native corn starch (Cargill, Minneapolis, Minn.),
surfactant (Excel P-40S), plasticizer (sorbitol), and polyvinyl alcohol
(Elvanol 51-05) was made at a ratio of the 38 parts of starch, 30 parts
polyvinyl alcohol, 2 parts of surfactant, and 30 parts of plasticizer. A
Hobart mixer was used for mixing. The mixture was then added to a K-Tron
feeder (K-Tron America, Pitman, N.J.) that fed the material into a ZSK-30
co-rotating, twin-screw extruder as described above. The first barrel #1
received the mixture at 20 lbs/hr when the extruder was heated to a
temperature for zones 1 to 7 of 95° C., 125° C.,
140° C., 150° C., 150° C., 145° C., and
130° C., respectively. The screw speed was set at 150-160 rpm to
achieve a melt pressure of 530-550 psi and a torque of 80-90%. In some
cases, a vent was also opened release steam generated due to the presence
of the added water in the plasticizer and inherent moisture in the
starch. The strands cooled down through a cooling belt (Minarik Electric
Company, Glendale, Calif.). A pelletizer (Conair, Bay City, Mich.) was
used to cut the strands to produce pellets, which were then collected and
sealed in a bag.

Example 6

[0080] A blend of hydroxypropylated starch and polyvinyl alcohol was
formed as follows. Initially, a mixture of a hydroxypropylated starch
(Glucosol 800), surfactant (Excel P-40S), plasticizer (sorbitol), and
polyvinyl alcohol (Celvol 203) was made at a ratio of the 36 parts of
starch, 30 parts polyvinyl alcohol, 4 parts of surfactant, and 30 parts
of plasticizer. A Hobart mixer was used for mixing. The mixture was then
added to a K-Tron feeder (K-Tron America, Pitman, N.J.) that fed the
material into a ZSK-30 co-rotating, twin-screw extruder as described
above. The first barrel #1 received the mixture at 10 lbs/hr when the
extruder was heated to a temperature for zones 1 to 7 of 95° C.,
125° C., 140° C., 150° C., 150° C.,
145° C., and 130° C., respectively. The screw speed was set
at 150-160 rpm to achieve a melt pressure of 530-550 psi and a torque of
80-90%. In some cases, a vent was also opened release steam generated due
to the presence of the added water in the plasticizer and inherent
moisture in the starch. The strands cooled down through a cooling belt
(Minarik Electric Company, Glendale, Calif.). A pelletizer (Conair, Bay
City, Mich.) was used to cut the strands to produce pellets, which were
then collected and sealed in a bag.

Examples 7-9

[0081] Various combinations of the starch of Example 1 and the polyvinyl
alcohol of Examples 2-3 were compounded with an Ecoflex® F BX 7011
resin (BASF, Florham Park, N.J.) using the ZSK-30 twin screw extruder
described above. The strands from the die was pelletized. The extrusion
conditions are set forth below in Tables 1-2:

[0082] Glucosol 800 starch, Elvanol 51-05, sorbitol, and surfactant (Excel
P-40S) were initially mixed in a Hobart mixer at 36%, 30%, 30%, and 4%,
respectively. The mixture was fed into ZSK-30 using K-Tron feeder.
Separately, Ecoflex® F BX 7011 resin (BASF, Florham Park, N.J.) was
fed from another K-Tron feeder into ZSK-30 for single-step compounding.
This process reduces the thermal degradation of materials during blend
preparation. The strands from the die were pelletized. The extrusion
conditions are set forth below in Table 3 and 4.

[0083] Plasticized hydroxypropylated starch from Example 1, plasticized
polyvinyl alcohol (Aqua-Sol® 116, which is available from A. Schulman,
Inc.), and Ecoflex®F BX 7011 resin (BASF, Florham Park, N.J.) were
compounded at varying ratios using the ZSK-30 twin screw extruder
described above. The strands from the die were pelletized. The extrusion
conditions are set forth below in Table 5.

[0086] As indicated, the film of Examples 1-3 (thermoplastic modified
starch, plasticized Elvanol 51-05, and Celvol 203) were brittle as
indicated by their high modulus values. The elongation for the film of
Example 1 (thermoplastic modified starch film) was particularly low in
comparison to those in Example 2 and 3 (plasticized PVA). The films of
Example 7, 8, 10˜12 (contained Ecoflex®) likewise had a low
modulus and high elongation, i.e., above 200%. The film peak stress was
very close to each other among the different films. The films of Example
13˜15 (containing Aqua-Sol® 116) had a lower modulus than those
shown in Example 7˜9, while the elongations values were comparable.
Furthermore, as also indicated in Table 7, each of the film samples
visibly disintegrated in tap water in less than 11/2 minute except for
Example 12, which took about 60 minutes for the film to disperse in
water.

[0087] While the invention has been described in detail with respect to
the specific embodiments thereof, it will be appreciated that those
skilled in the art, upon attaining an understanding of the foregoing, may
readily conceive of alterations to, variations of, and equivalents to
these embodiments. Accordingly, the scope of the present invention should
be assessed as that of the appended claims and any equivalents thereto.